Human gp130 protein

ABSTRACT

Human gp130 protein having at least the following properties: (1) the protein has an affinity with a complex of IL-6 (interleukin-6) and an IL-6 receptor (interleukin-6 receptor); (2) the protein shows an apparent molecular weight of 130 kDa in SDS-polyacrylamide electrophoresis; and (3) the protein participates in the transmission of IL-6 signal; DNA coding for the protein, an expression plasmid containing the DNA; and a process for production of the protein using the expression plasmid.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a human gp130 protein, which is a protein participating in the transmission of an IL-6 signal, a DNA coding for this protein, and a means for and a method of producing this protein by genetic engineering.

2. Description of the Related Art

Interleukin-6 (IL-6) is a protein participating broadly in the proliferation and differentiation of an organism, and is characterized in that the protein plays an important role in defense system of an organism such as immunity, hematopoiesis or inflammation (see Kishimoto, Blood, 74, page 1, 1989). It is reported that an abnormal production of IL-6 may become a factor in the cause of various autoimmune diseases (see Kishimoto and Hirano, Ann. Rev. Immunol., page 485, 1988).

The inventors isolated a gene for human IL-6 receptor on the cell membrane, which is specifically bonded to human IL-6, and determined the primary structure thereof (see Japanese Patent Application No. 63-194885). Then the inventors isolated a gene of mouse IL-6 receptor on the cell membrane, which is specifically bonded to mouse IL-6, and determined the primary structure thereof (see Japanese Patent Application No. 1-292230). Furthermore, the inventors prepared a soluble IL-6 receptor (extracellular portion of an IL-6 receptor), considered to be usable for a therapeutic or diagnostic medicine, from the human IL-6 receptor gene as the starting material (see Japanese Patent Application No. 1-9774).

SUMMARY OF THE INVENTION

An artificial control of the function of IL-6 strongly exerting physiological activities in a organism is considered usable as a new mechanism for the therapy of various diseases, and knowledge of the course of the transmission of an IL-6 signal is important in the development of a medicinal substance for enhancing or inhibiting the function of IL-6.

The inventors investigated the mechanism of the transmission of IL-6 signal, and as a result, found that, in addition to the IL-6 and IL-6 receptor, there exists, as a third factor, a protein participating in the transmission of IL-6 signal. Since this protein has an apparent molecular weight of 130 kb, the inventors named this protein "human gp130". To further analyze the transmission of IL-6 signal or to develop a soluble gp130 (the extracellular portion of a gp130 protein) as an inhibitor for IL-6, a large quantity of a purified product of soluble gp130 must be obtained but the amount of gp130 produced in an organism is very small. A DNA sequence coding for pg130 is indispensable for producing gp130 in a large quantity by a genetic engineering method.

Therefore, a primary object of the present invention is to provide a human gp130, a DNA coding for the gp130, and a process for producing the gp130 by using the DNA.

The inventors carried out research into the transmission of IL-6 signal, and found a protein on the cell membrane which participates in the transmission of IL-6 signal, and furthermore, proved that the IL-6 receptor on the cell membrane is bonded to this membrane protein through the bonding to IL-6, this membrane protein bears the transmission of IL-6 signal, and the intracellular region of the IL-6 receptor does not participate in the transmission of IL-6 signal.

Also, the inventors succeeded in cloning a DNA coding for human gp130, and determined the nucleotide sequence of this DNA.

The present invention is based on the results of these researches. More specifically, the present invention provides a gp130 participating in the transmission of IL-6 signal; a DNA sequence coding human gp130; a replicable vector capable of expressing this DNA sequence in a recombination microorganism or cultured cell; a microorganism or cultured cell transformed by this expression vector; and a process for the production of human gp130, which comprises expressing a DNA sequence coding gp130 in this microorganism or cultured cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows autoradiographic patterns obtained when U266 cells internally labelled with ³⁵ S-methionine are lysed after treatment with IL-6 (lanes 2 and 4) or without treatment with IL-6 (lanes 1 and 3), and then immunoprecipitated by an IL-6 receptor antibody MT18 immobilized on Sepharose B4, and SDS/PAGE is carried out under non-reducing conditions (lanes 1 and 2) or under reducing conditions (lanes 3 and 4);

FIG. 2 shows autoradiographic patterns obtained when M12IL6R cells surface-labelled with ¹²⁵ I are lysed after treatment with IL-6 (lane 2) or without treatment with IL-6 (lane 1), and is then treated in the same manner as in FIG. 1;

FIG. 3 shows autoradiographic patterns obtained when M12 cells are incubated in the presence (lanes 2 and 4) or absence (lanes 1 and 3) of IL-6 and in the presence of a culture supernatant of COS7 cells containing soluble IL-6 receptor (lanes 3 and 4) or not containing soluble IL-6 receptor (lanes 1 and 2) and lysed, and is then treated in the same manner as in FIG. 1;

FIG. 4 shows incorporation of ³ H-labelled thymidine by MI cells in the presence of IL-6 at various concentrations, and in the presence or absence of a soluble IL-6 receptor;

FIG. 5 shows a restriction enzyme map of λA and λB and a schematic structure of a corresponding human gp130 protein, in which E represents the EcoRI site, SS represents the signal sequence, EC represents the extracellular region, TM represents the membrane penetration region, and C represents the intracellular region;

FIG. 6 shows the structure of pGP130;

FIGS. 7-1 through 7-6 show the results of the analysis of the nucleotide sequence of insert DNA of pGP130, i.e., DNA coding for human gp130, and show the presumed amino acid sequence of a protein, i.e., human gp130 produced when this DNA sequence is expressed, in which the underlined portion represents a hydrophobic amino acid region on the N-terminal side and the double-underlined portion represents a hydrophobic amino acid region on the C-terminal side; and,

FIG. 8 shows the results of a Northern blot analysis of various cells conducted by using human gp130 cDNA as the probe.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

1. gp130 Protein

The cell membrane-derived protein participating in the transmission of IL-6 signal according to the present invention, i.e., gp130, exerts an important function when IL-6 is bonded to an IL-6 receptor to finally cause various cells to exert biological activities such as proliferation and differentiation, and in the natural state, this protein is located on the cell membrane. The IL-6 referred to herein includes IL-6 produced in an organism, IL-6 produced by a genetic engineering method, and derivatives thereof. Furthermore, the IL-6 receptor includes a IL-6 receptor present on the cell membrane produced in an organism or by a genetic engineering method, a soluble IL-6 receptor isolated from the cell membrane, and derivatives thereof.

This protein has the following properties.

(1) The protein is bonded to a complex of IL-6 and an IL-6 receptor.

(2) The protein is not bonded to IL-6 alone or IL-6 receptor alone.

(3) The protein shows an apparent molecular weight of 130 kDa in the SDS-polyacrylamide gel electrophoresis. This protein participates in the transmission of IL-6 signal and in the natural state, has an amino acid sequence (referred to herein as formula (I)) of from Met at 1-site to Gln at 918-site in FIG. 7. In the present invention, the protein may be any protein having the above-mentioned amino acid sequence, and a protein or polypeptide having a portion of the above-mentioned amino acid sequence that makes a contribution to the specific bonding to a complex of IL-6 and IL-6 receptor. Namely, all proteins and polypeptides having an amino acid sequence in which at least one amino acid residue of the above-mentioned amino acid sequence is substituted by another amino acid residue(s), or at least on amino acid residue is deleted from the above-mentioned amino acid sequence, or at least one amino acid is added to the above-mentioned amino acid sequence, and still retaining a capacity of being specifically bonded to complex of IL-6 and IL-6 receptor, are included within the scope of the pg130 of the present invention. For example, there can be mentioned proteins in which an amino acid sequence or amino acid residue not making a contribution to the bonding to the complex of IL-6 and IL-6 receptor in the above-mentioned amino acid sequence is modified by substitution, deficiency or insertion, proteins in which an amino acid sequence and/or an amino acid residue portion is added to the N-terminal side and/or the C-terminal side of the above-mentioned amino acid sequence, and proteins formed by a fusion of another protein, such as a human growth hormone, to the above-mentioned amino acid sequence.

The amino acid sequence represented by formula (I) consists of 918 amino acid residues, and hydrophobic amino residues are located in the region of from leucine at the second position from the N-terminal side to glycine located at the 22nd position and the region of from alanine at the 620th position to phenylalanine at the 641st position. It is considered that, of these two regions, the former region is a signal peptide region and the latter region is a membrane penetration region.

2. DNA Sequence

DNA coding for human gp130 protein of the present invention encodes, for example, an amino acid sequence of from Met at 1-position to Gln at 918-position in FIG. 7. Representative cDNA has a base sequence of from A at 273-position to G at 3026-position in FIG. 7. The DNA sequence of the present invention includes not only the above-mentioned DNA sequence but also DNA in which at least one nucleotide of the above-mentioned DNA sequence is substituted with another nucleotide, or at least one nucleotide is deleted from the above-mentioned DNA sequence, or at least one nucleotide is added to the above-mentioned DNA sequence, and which codes for a protein having a capacity of being specifically bonded to the IL-6/IL-6 receptor complex. For example, there can be mentioned DNA sequences coding proteins having the amino acid sequences as mentioned in (1) above.

3. Process for Preparation of gp130 Protein

According to the first process of the present invention, the cell membrane-derived protein participating in the transmission of IL-6 signal is prepared from animal cells producing this protein. As the cells, there can be mentioned IL-6 receptor-producing cells, for example, human myeloma cell U266, mouse leukemia cell line M1, and human B cell line CL4. The protein of the present invention participating in the transmission of IL-6 signal also can be produced by cells not producing IL-6 receptor. As the cells of this type, mouse B cell line M12, human T cell line Jurkat, and mouse T cell line CTLL2 can be mentioned. Namely, the protein participating in the transmission of IL-6 signal according to the present invention can be obtained from these cells.

As pointed out hereinbefore, the protein of the present invention is bonded to the IL-6 receptor in the presence of IL-6 but is not bonded to the IL-6 receptor in the absence of IL-6, and therefore, the protein of the present invention can be isolated by utilizing this property.

For example, to isolate the protein from cells producing both the IL-6 receptor and the protein of the present invention, a process can be adopted in which the producing cells are cultured, IL-6 is artificially added to the cultured cells, incubation is carried out for a time sufficient to allow a reaction between the cells and the added IL-6 under physiological conditions, for example, for about 30 minutes at about 37° C. in a conventional culture medium such as RPMI1640, and the cells are then lysed by a customary method, for example, by a treatment with a triethanolamine buffer solution containing 1% of digitonine, whereby a cell lysate containing a complex in which IL-6, the IL-6 receptor and the protein of the present invention are bonded together is obtained. Alternatively, after the cells are lysed by a customary method, incubation is carried out in the above-mentioned manner to obtain a cell lysate containing the above-mentioned complex. An antibody to IL-6 receptor, for example, MT18 antibody (prepared according to Referential Example 1 given hereinafter; see Japanese Patent Application No. 63-194885) is immobilized by a solid carrier, for example, Sepharose 4B, by the cyanogen bromide activation method. By placing this immobilized antibody to IL-6 receptor in contact with the above-mentioned cell lysate, the complex containing the protein of the present invention is immobilized on the above-mentioned solid carrier through the specific reaction between the IL-6 receptor and the IL-6 receptor antibody. Then, this solid carrier is washed to remove non-specifically bonded or adhering impurities, and the complex is eluted from the solid carrier by a conventional means using, for example, urea or guanidine, to free the desired protein of the present invention from the IL-6 receptor-containing protein complex.

To isolate and purify the desired protein of the present invention from the obtained solution, customary means adopted for the isolation and purification of proteins, such as precipitation using ammonium sulfate, column chromatography, for example, reversed phase chromatography and ion exchange chromatography, and electrophoresis can be used. During this isolation and purification process, an active fraction can be selected by utilizing the bonding to the IL-6 receptor in the presence of IL-6, non-bonding to the IL-6 receptor in the absence of IL-6, and confirming the molecular weight of 130 kDa as the criterion.

Where cells producing the protein of the present invention but not producing the IL-6 receptor are used, incubation is carried out in the presence of a soluble IL-6 receptor and IL-6, and the cells are then lysed to obtain a cell lysate containing an IL-6/IL-6 receptor/desired protein complex. Alternatively, the above-mentioned cells producing the protein of the present invention are lysed, an incubation of IL-6 and the IL-6 receptor is carried out, and finally, a cell lysate containing an IL-6/IL-6 receptor/desired protein complex is obtained. The desired protein can be isolated and purified from this cell lysate in the above-mentioned manner.

The second process for the production of the protein participating in the transmission of IL-6 signal according to the present invention utilizes gene recombination. In this process, DNA coding for an amino acid sequence of a protein on the cell membrane, which participates in the transmission of IL-6 signal, can be obtained by various methods. For example, cDNA library is formed from cells expressing the above-mentioned protein thereon, such as human myeloma cells, according to customary procedures, and this library is selected according to various methods, for example, the method in which a probe designed on the basis of a partial amino acid sequence of the purified protein is used, and the method in which cDNA is expressed and the selection is made based on the property of the produced protein, for example, the specific bonding to the IL-6-bonded IL-6 receptor. The protein of the present invention is produced by expressing the thus-cloned DNA according to customary procedures.

4. DNA Coding gp130 Protein

The DNA to be used for the above-mentioned process can be prepared based on desired messenger RNA selected from various messenger RNA's extracted, for example, from the human placenta by a known method, by using a probe prepared based on the DNA sequence of FIG. 7 provided by the present invention. Alternatively, a part or all of this DNA can be chemically synthesized according to the disclosure of the present invention.

5. Expression Vector

As the replicable expression vector capable of expressing the DNA sequence coding human gp130 provided according to the present invention, any vector having a replicating origin, control sequences and a sequence coding for gp130, and capable of transforming a selected host can be appropriately used without limitation. For example, plasmids such as pBR322 and pBR327 can be used when E. coli is used as the host, and when cultured cells of a mammal or the like is used as the host, a vector having a DNA replicating origin derived from SV40 virus, can be used.

Of the control sequences for expressing the coding sequence, promoter system is important, and an appropriate promoter system should be elected according to the relationship to the selected host. When E. coli is used as the host, lactose promoter system, a tryptophan promoter system and hybrid promoter systems thereof are preferably selected. When cultured cells derived from a mammal are used as the host, an SV40 promoter system, adenovirus promoter system, and cytomegalovirus promoter system are preferably selected.

6. Host

Microorganisms or cultured cells customarily used for producing proteins by genetic engineering can be used as the host without limitation. As the microorganism, there can be mentioned E. coli such as K-12 or W-3110, Bacillus subtilis and yeast, and as the cultured cells, there can be mentioned COS cells (monkey renal fibroblast), CHO cells (Chinese hamster oocyte), and myeloma cells.

The host explained in (4) above, which has been transformed by the vector explained in (5) above, is cultured to express the DNA sequence coding for human gp130 in the vector DNA, whereby human gp130 is produced. This is realized by the activation of the promoter system in the control sequences linked to the DNA sequence coding for human gp130.

A polyclonal antibody or monoclonal antibody to the protein of the present invention can be prepared according to customary procedures by using the protein of the present invention prepared according to various processes as described above, or the cell producing this protein as an immunogen. As the cell source and animal to be used in this preparation process, there can be mentioned organisms such as human, mouse, rabbit, goat, and sheep.

The cell membrane-derived protein participating in the transmission of IL-6 signal, provided according to the present invention, can be used as a reagent for clarifying the signal transmission mechanism of IL-6 and developing valuable substances such as therapentic agents for controlling the function of IL-6. For example, by using, as a detection criterion, the property of the present protein which transmits IL-6 signal while being specifically bonded to the IL-6 receptor bonded to IL-6, substances controlling the function of IL-6 can be screened. As the substances to be screened, there can be mentioned natural substances, synthetic chemicals, IL-6 and an IL-6 receptor produced by a genetic engineering, derivatives thereof, and antibodies to IL-6, the IL-6 receptor, and antibodies to these proteins.

Furthermore, by bonding the soluble IL-6 receptor which has been bonded to IL-6 to the present protein, the function of IL-6 can be enhanced, and the function of IL-6 can be exerted even on a cell having no IL-6 receptor in the cell surface layer. On the other hand, if the bonding of the above-mentioned protein to the IL-6 receptor which has been bonded to IL-6 is inhibited by an antibody to IL-6, IL-6 receptor or the above-mentioned protein, the biological activity of IL-6 will be inhibited. Accordingly, it is considered that the protein of the present invention will be usable as an active ingredient of a medicine.

Furthermore, by the DNA sequence coding for human gp130 according to the present invention, and the means and process for producing this protein by genetic engineering, this protein, which is produced only in a very small amount in the natural state, can be produced in a large quantity.

The present invention will now be described in detail with reference to the following examples, that by no means limit the scope of the invention. Note, the protein of the present invention is sometimes called "gp130" in the examples for convenience.

EXAMPLE 1 Bonding of Protein (gp130) on Human Cell Membrane to Human IL-6 Receptor in Presence of Human IL-6

Human myeloma cells U266 (cells producing the IL-6 receptor and gp130 protein) (2×10⁷ cells) were internally labelled with 1 mCi of ³⁵ S-methionine and divided into two parts. One part was incubated in 0.5 ml of PRMI1640 at 37° C. for 30 minutes in the presence of IL-6 (1 μg/ml), and the other part was similarly incubated in the absence of IL-6. Then, the U266 cells were lysed with 1 ml of a 10 mM triethanolamine buffer solution (having a pH value of 7.4) containing 1% of digitonine (supplied by Wako Junyaku), 0.15M NaCl, and 1 mM pAPMSF (supplied by Wako Junyaku). Separately, the IL-6 receptor antibody MT18 (Referential Example 1) was bonded to Sepharose 4B activated by cyanogen bromide, and the bonded antibody then mixed with the supernatant of the above-mentioned cell lysate, whereby the solubilized IL-6 receptor was bonded to the MT18 antibody on the resin.

The non-specifically bonded substances were washed away by the above-mentioned solution containing 1% of digitonine. Then, under reducing or non-reducing conditions, the polyacrylamide gel electrophoresis in sodium dodecyl sulfate (SDS/PAGE) and the autoradiography were carried out. The results are shown in FIG. 1. In FIG. 1, the band of 80 kDa shows the ³⁵ S-methionine-labelled IL-6 receptor derived from the U266 cell, and the band of 130 kDa shows the gp130 protein of the present invention. From the results shown in FIG. 1, it is seen that the IL-6 receptor bonded to IL-6 is bonded to the human protein (gp130) having a monomer molecular weight of 130 kDa within 30 minutes at 37° C.

EXAMPLE 2 Bonding of Human IL-6 receptor to Protein (gp130) on Mouse Cell Membrane in Presence of Human IL-6

A plasmid prepared by inserting a human IL-6 receptor cDNA into the site of BamHI in the plasmid pZipNeoSV(X)I (see Cepko et al, Cell, 37, page 1053, 1984) was introduced into a mouse B cell strain M12 not expressing the IL-6 receptor on the cell surface, by the electropolation method, and the transformed cell was screened based on the resistance to an antibiotic substance G418 (supplied by Sigma). The thus-established mouse B cell M12-derived clone expressing the human IL-6 receptor on the cell surface was named "M12IL6R".

Then, 10⁷ of M121L6R cells were washed with PBS and suspended in 0.1 ml of 50 mM Tris (having a pH value of 7.4) and 0.15M NaCl. Next, 1 mCi of Na ¹²⁵ I and two Iodobeads (supplied by Pierce) were reacted at room temperature for 5 minutes in 0.1 ml of the above-mentioned buffer solution, the reaction liquid was mixed with the above-mentioned cell suspension, and incubation was carried out at room temperature for 30 minutes. Then 1 μg/ml of IL-6 was added to the thus-labelled cells, or was not added, and the reaction was carried out at 37° C. for 30 minutes, the cell was lysed according to the method described in Example 1, an immunoprecipitation by MT18 was carried out, and the SDS/PAGE and autoradiography were then carried out. The results are shown in FIG. 2. In FIG. 2, the band of 80 kDa shows the IL-6 receptor produced by the IL-6 receptor cDNA introduced into an M12 cell, and the band of 130 kDa shows a gp130 protein inherently produced by the M12 cell. From the results shown in FIG. 2, it is seen that the human IL-6 receptor on M12IL6R bonded to the human IL-6 is bonded to the mouse protein (gp130) derived from M12IL6R, at 37° C. within 30 minutes.

EXAMPLE 3 Bonding of Soluble IL-6 Receptor to gp130 in Presence of IL-6

According to the method described in Example 2, 2×20⁷ of M12 cells (cells not producing IL-6 receptor) were labelled, 5×10⁶ of the labelled cells were added to 1 ml of a culture supernatant of COS7 cells containing or not containing the soluble IL-6 receptor in the presence or presence of IL-6 (1 μg/ml), and the reaction was carried out at 37° C. for 30 minutes. Then the cells were lysed with digitonine according to the method described in Example 1, immunoprecipitation was carried out by MT18 antibody, and the SDS/PAGE and autoradiography were then carried out. The results are shown in FIG. 3. In FIG. 3, the band of 130 kDa shows the gp130 protein produced by M12 cells. Note, in this example, since the soluble IL-6 receptor was not labelled, this receptor was not shown by the autoradiography. From the results shown in FIG. 3, it is seen that the complex of IL-6 and the soluble IL-6 receptor is bonded to the protein (gp130) on the cell membrane, and the soluble IL-6 receptor alone is not bonded to gp130.

EXAMPLE 4 Enhancement of Function of IL-6 by Soluble IL-6 Receptor in Presence of IL-6

M1 cells (1×10⁵ cells/ml) were cultured at 0.2 ml/well in a culture medium containing IL-6 at various concentration as well as COS7 cell supernatant or soluble IL-6 receptor-containing COS7 cell supernatant in an amount of 25%. Within 60 to 70 hours from the start of the culturing, ³ H-labelled thymidine was added, and by measuring the radioactivity incorporated into the cells, the proliferation of the cells was examined. FIG. 4 shows that the effect of inhibiting the proliferation of M1 cells, possessed by IL-6, is enhanced by the soluble IL-6 receptor. Namely, the function of IL-6 is enhanced by the bonding of the IL-6-bonded soluble IL-6 receptor to gp130 of M1 cell.

EXAMPLE 5 Isolation of Human gp130 cDNA

A series of gene recombination operations (extraction of m-RNA, cleavage of DNA by restriction enzyme, and the like) were carried according to the process of Maniatis et al (see Molecular Cloning, Cold Spring Harbor Laboratory, 1982) and the process of Harwin et al (see DNA Cloning, A Practical Approach, vol. 1, page 49, IRL, Oxford, 1985). Screening by the antibody of λgt11 cDNA library was carried out according to the conventional method.

First, a messenger (m) RNA was extracted from human myeloma cell U266 (see Cell, volume 58, page 573, 1989), and a cDNA library was prepared by using λgt11 (supplied by Clontech). Then, using mouse-derived monoclonal antibodies AM64 and AM277 (see Japanese Patent Application No. 2-15090) to gp130, about 500,000 clones were screened, and finally, two coulones (λ_(A) and λ_(B)) were obtained. The insert cDNA of each of λ_(A) and λ_(B) was analyzed, and the results are shown in FIG. 5. As shown in FIG. 5, the insert cDNAs did not contain the full length human gp130-coding region.

Accordingly, an EcoRI fragment of λ_(A) and the EcoRI fragment of λ_(B) were inserted, while connecting them in the orientation of reading of cDNA, to the EcoRI site of a vector pBlueScript SK (supplied by Stratagene) to prepare a plasmid pGP130 having an insert DNA containing the complete human gp130-coding region. The structure of pGP130 is shown in FIG. 6, and the sequence of the insert DVA of pGP130, i.e., the sequence of human gp130 cDNA determined from insert cDNA sequences of λ_(A) and λ_(B), and the presumed amino acid sequence, are shown in FIG. 7.

Note, E. coli HB101/pGP130 containing this plasmid pGP130 was internationally deposited as deposition No. FERM BP-2912 under the Budapest Treaty on May 15, 1990 with the Fermentation Research Institute, Agency of Industrial Science and Technology, located at 1-3, Higashi 1-Chome, Tsujuka-shi, Ibaragi-ken, Japan.

EXAMPLE 16 Expression of Human gp130 mRNA in Various Cells

To examine the expression of human gp130 in various cells, Northern blot analysis was carried out. The culturing of cells, extraction of mRNA from the cells, electrophoresis, blotting, probe labelling, hybridization, filter washing, and autoradiography were carried out according to standard methods.

mRNA was extracted from human myeloma cells U266, human B cells CESS, human Burkitt's lymphoma Jijoye, human T cells Jurkat, and NK cells YT, and 1 μg of each mRNA then denaturated by the formamide method and subjected to electrophoresis with 0.8% agarose gel, and to Northern blotting on a nylon filter membrane. Then an insert cDNA of λ_(A) obtained by the method described in Example 5 was extracted, and using this extracted insert cDNA, hybridization was carried out at 42° C. for 24 hours. The product was then washed and autoradiography was carried out.

The results are shown in FIG. 8, and it is seen that the manifestation of gp130 mRNA is strong in U266 and YT, medium in CESS, and weak in Jijoye and Jurkat. This has a relation to the reactivity of the IL-6 of each cell.

REFERENTIAL EXAMPLE 1 Preparation of Monoclonal Antibody to Human IL-6 Receptor

To prepare a mouse monoclonal antibody to human IL-6 receptor, a mouse T cells having human IL-6 receptors expressed on the cell membrane surface was prepared as an antigen, according to the following method. More specifically, pBSF2R.236 and pSV2neo disclosed in Japanese Patent Application No. 1-9744 were introduced in mouse T-cells CTLL-2 (ATCC, TIB214) according to a customary procedure, and screening was carried out according to the conventional method using G-418. Finally, the strain in which about 30,000 IL-6 receptors per cell were expressed was established, and this strain was named "CTBC2".

The immunization was carried out in the following manner. The CTBC2 cells were cultured according to a conventional method using PMRI1640, and the cultured CTBC cells were washed four times with a PBS buffer and used intraperitoneally to immunize C57BL6 mouse in an amount of 1×10⁷ cells per mouse once a week, six times as a whole.

The spleen cells of the immunized mouse were fused to the myeloma cells P3U1 as the parent cell line, according to a conventional method using polyethylene glycol.

Screening was carried out in the following manner. Namely, pBRF2R.236 and PSV2neo were introduced into the IL-6 receptor-negative human T cell strain JURKAT (ATCC, CRL8163) according to a conventional method, and by the screening, a strain expressing about 100,000 IL-6 receptors per cell was established, and this stain was names "NJBC8". One clone of the hybridoma producing an antibody recognizing NJBC8 lysed by NP40 but not recognizing JURKAT lysed by NP40 was isolated and named "MT18". The monoclonal antibody produced by this hybridoma was named "MT18 antibody".

The above-mentioned hybridoma MT18 was deposited at the Fermentation Research Institute (FRI) Agency of Industrial Science and Technology 1-3 Yatabe-cho Higashi 1-chome Ibaraki Japan as FERM P-10840 on Jul. 12, 1989, and transferred to an international deposition under the Budapest Treaty as FERM BP-2999 on Jul. 10, 1990. 

I claim:
 1. A substantially purified and isolated protein comprising human gp130 protein, wherein said protein:(1) has a monomeric molecular weight of approximately 130 kDa in SDS-polyacrylamide electrophoresis; (2) is associated with the cell membrane; and (3) is capable of forming a complex with IL-6 and an IL-6 receptor which is required in order for IL-6 to induce cellular proliferation and differentiation.
 2. A human gp130 protein according to claim 1, wherein said protein consists essentially of an amino acid sequence from Met at the 1st site to Gln at the 918th position in FIG.
 7. 3. A human gp130 protein according to claim 1, wherein said protein is produced using DNA encoding said protein. 